**Abstract**

The light-struck taste (LST) of wine is a defect that mainly occurs in bottled wines exposed to light. Factors that influence the onset of the LST in wines were reported. The effect of grapes and wine composition, the alcoholic fermentation process, the yeast strains used and the conditions of yeast nutrition were included. The external factors, such as bottle color, time and nature to light exposure and type of closure were considered. Finally, the analysis of the main molecules related to this default (sulfur volatile compounds and their amino acids and riboflavin precursors) and possible prevention measurements were also exposed.

**Keywords:** amino acids, wine, riboflavin, aroma, LEDs, stoppers, sensory analysis

### **1. Introduction**

The light-struck taste (LST) of wine is a defect that mainly occurs in white and rosé bottled wines exposed to light for a considerable period of time. The lightinduced changes in wines are mainly due to photochemical reactions but several factors can influence it. The most important are related to the wine composition, the spectrum of the light source, the intensity of the radiation, the optical properties of the glass bottle and the irradiation time. The wine composition alterations caused by these factors lead to detrimental effects on the sensory attributes. In bottled wine, the exposure to light can cause a significant browning effect and bring about unpleasant smells [1–5]. These bad effects were due to the photochemical oxidation involved in this deterioration which can affect phenolic substances, acids, alcohols and other wine compounds [6, 7].

In particular, riboflavin (RF) or vitamin B2 is one of the most important precursors in the generation of aromas related to the LST. This is a highly photosensitive molecule, which can undergo photochemical degradation through different ways. In addition, sulfur amino acids are involved in the photo-reduction of riboflavin being also important precursors in the appearance of sulfur volatiles. That is why, both methionine and cysteine (the sulfur amino acids of wine) in the presence of riboflavin (**Figure 1**) can suffer photo-oxidative degradation giving raise to unpleasant aromatic volatile sulfur compounds (VSCs), such as hydrogen sulfide, methanethiol, dimethyl sulfide and dimethyl disulfide (**Figure 1**). The combination of these aromatic sulfur compounds leads to the defect called 'light struck taste', 'taste of light' or in French 'goût de lumière'. Wines with this default presents unpleasant aromas described as rotten egg, garlic, onion, boiled cabbage and sometimes also provides a metallic taste perception. Given the importance of this defect and the economic losses that it may entail, both oenological and photovoltaic strategies are

**Figure 1.** *Molecular structures of precursors and aromatic compounds related to the LST default.*

currently being sought to prevent the appearance of this default in bottled wines stored in wineries, supermarkets or wine bars, in order to offer consumers an optimal wine quality.
